I made something similar for Philadelphia

https://play.google.com/store/apps/details?id=com.staticfish...

Wow, I knew they rolled out some access to countdown from the ibus system, but I thought hell would freeze over before they'll allow people to track tube locations.

Its probably not the actual location of the tube, but a guestimate based on the departure time, arrival time and the distance between stations.

It depends on the line. The more modern lines, have induction loops every 3 meters that allow precise measurement of current position, and also data for voice comms to the line controller.

On older lines, they can only detect when a tube changes power circuit and the resulting blue/white spark sends a measurable pulse down the power system. In this case, yes, they have to just count trains into and out of a section.

I learnt this by chatting to a TFL engineer in a pub, he designed the signalling systems equipment.

Used the tube map app while visiting London and it was incredibly helpful. Great to see this new improvement.

Very cool. Free app tried, paid app bought!